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Bumblebees really, really like purple and now we know why. Experiments show that their inborn colour preference gives them a good start in life.

"The world's a bit of a tough place for a naive bee," says Dr Adrian Dyer, a research in how animals perceive colour from La Trobe University in Australia. "They have to go out and find the goodies."

Any bee that innately prefers the colour of flowers with the highest amounts of nectar will probably have a better chance of surviving its first few days in the world and then pass on that trait to its own offspring.

Under laboratory conditions, researchers compared the colours of specific species of flowers found near Würzburg in Germany, their nectar content and the colour preferences of local newborn naive Bombus terrestris bumblebees.

Dr Nigel Raine and Professor Lars Chittka at Queen Mary, University of London found that there is a clear advantage to bees that start out life primed for purple.

"The purple flowers in that area near Würzburg are more rewarding," says Raine.

By rewarding, he means they are unusually nectar-rich. Similar colour preferences are found, but not previously explained, in several other bumblebee species from Asia, Europe and North America, Raine says.

But just because bumblebees come preloaded with a purple preference, doesn't mean they are slaves to it, Raine says.

"They're very flexible in their foraging behaviour," he says. "They can change their preference."

Unlike the purple preference, bees have to learn the advantages of flowers of other colours by going out into the world and checking out what's there.

The chicken or the egg?

Among the practical questions the new study may answer says Dyer is a longstanding chicken-or-egg matter.

Have flowers evolved and changed colours to attract the bees, or have bees evolved preferences that serve flowers?

The purple preference implies that some bees probably just had an individual, natural preference for purple flowers that turned out to be advantageous and inheritable.

Because it served the bumblebees well, it led to more bees with the preference successfully reproducing until all bumblebees had the preference.

"It's not the case that the bees had the preference first and the flowers followed," says Dyer.

This could have important implications for places like Australia, where bumblebees have not yet taken up residence, but could in the near future, he says. Tasmania saw its first bumblebees just 15 years ago, he notes.

The fact that flowers elsewhere seem to push bumblebees to evolve preferences could mean, for instance, that the flora of Australia might change the bumblebees more than vice versa.